This invention relates to the separation of fluid phases, for example the separation of particulate matter from gases such as air.
Standard cyclone separators cause the incoming fluid mixture to swirl around a chamber so that phases separate radially due to the accelerations towards the axis, the separated phases being removed through separate outlets at different radii. Besides the chamber in which separation takes place, an inlet chamber may be provided in which linear motion of the fluid mixture is converted into swirling motion. This has normally been arranged by making the inlet chamber a cylinder with a linear inlet conduit entering the periphery of the cylinder along a tangent, so that the fluid from the inlet conduit then swirls about the cylinder axis.
The change from linear motion to motion around the inside of the cylinder involves an abrupt change of curvature of the path from zero to the curvature of the cylinder, which may cause turbulence in the flow. We have found a construction of separator in which the change is less abrupt, so that a free vortex is more likely to be found. Continuing increases of curvature enable the flow to be concentrated.
According to the invention there is provided a cyclone separator having an inlet chamber and an outlet chamber, means for introducing a fluid mixture into the inlet chamber so that it swirls around the chamber and passes to the outlet chamber in which it swirls about an outlet chamber axis, the outlet chamber being provided with means for conducting heavier phase fluids from the outlet chamber at a relatively large distance from the outlet chamber axis and an outlet for lighter phase fluids at a relatively small distance from the outlet chamber axis, at least one of the chambers being involute shaped, the corresponding one of said means being defined by the curved wall of the involute of maximum radius.
The involute shaped chamber is preferably the inlet chamber, although making both inlet and outlet chambers involute shaped is also an option. In this case the involutes preferably have a common axis and are arranged so that fluids flowing through them continue to swirl in the same sense about the axis. When he outlet chamber is involute shaped it is preferably that the near-axis outlet comprises a duct extending into the involute chamber (by say 25% of the chamber axial length) to form a vortex finder.
The involute shaped chamber preferably has a curved wall formed from at least three (and preferably four) arcuate portions of uniform curvature, each portion having a smaller curvature than the preceding inner portion, the adjacent portions having their centres on the common normal to the adjacent ends of those portions. An involute may have a maximum radius between 25% and 300% larger than the minimum radius.
An intermediate chamber may be provided between said means of the inlet chamber and of the outlet chamber through which the fluid can swirl in passing from the inlet chamber to the outlet chamber. It may be frusto-conical, preferably with an outlet radius at least half the inlet radius, and preferably with a length less than five times its inlet end diameter and more preferably less than its inlet end diameter.
We have found that an additional inlet in the upstream axial region of an involute chamber can be very useful. This is because the swirl imparted to the incoming mixture causes a low pressure in this axial region; the low pressure can therefore be used to draw in another fluid. The arrangement is very different from a jet pump, which normally has a low pressure inlet entering an axial chamber from one side and a high pressure inlet on the axis. In that case it is the axial high pressure inlet which causes a fluid to be drawn in from the side inlet. There is no effort made to induce swirl in such a jet pump.
When the additional inlet is so provided, it should preferably be of a radius not greater than 50% (and more preferably not greater than 25%) of the minimum radius of the inlet involute and smaller than any outlet on the axis of the outlet involute. Means can be provided for conducting some of the fluid from said means of the outlet chamber to this additional inlet arranged on the axis of swirl of fluid introduced by said means of the inlet chamber. This conducting means preferably includes a further separating stage for fluids from said means of the outlet chamber, the outlet from said further stage for lighter phases being conducted in use to said additional inlet. By passing through the further stage only some rather than all of the full flow through the second stage, it is possible to use a further stage of much smaller volume. The conducting means is preferably arranged to conduct all the fluid from said means of the outlet chamber to said further stage. The further stage could be a separator similar to those already described, or a conventional separator or even just a filter.
The driving force for moving the fluid through the third stage is provided by the low pressure existing at the additional inlet and so no additional energy is required; the driving force for moving the phase mixture through the separator as a whole may be in the form of a fan to draw the less dense fluid out of the separator. This has the advantage that the fan only has to deal with the lighter phases, whereas heavier phases might clog or damage it. Alternatively a pump may be provided to receive the fluid mixture before separation with its outlet connected to the fluid introducing means. A fan could be located between stages.